Metallic compounds for use in hightemperature applications



NIETALLIC COMPOUNDS FOR USE IN HIGH- TEMPERATURE APPLICATIONS Roger A.Long, Bay Village, Ohio (1782 Knoxville St., San Diego, Calif.)

No Drawing. Continuation of application Ser. No. 177,548, Aug. 3, 1950.This application Apr. 12, 1957,

Ser. No. 652,358

8 Claims. (Cl. 23-204 (Granted under Title 35, US. Code (1952), sec.266) This invention relates to metallic compounds which arecharacterized by a relatively high melting point, i.e. relatively highrefractoriness, and by resistance to oxidation and abrasion at elevatedtemperatures. lar the invention relates to inter-metallic compounds ofsilicon with certain metals of the fourth and sixth groups of theperiodic table of the elements. More-specifically the invention relatesto an inter-metallic compound of molybdenum di-silicide and to itsproperties and uses.

The general object of the invention is to produce an inter-metalliccompound or an intermediate solid solution of silicon and a metalselected from the group consisting of uranium, molybdenum, chromium,tungsten,

zirconium, and titanium by a novel method of heat.

treatment.

It is a further object of the invention 'to produce an inter-metalliccompound of silicon with one of the above defined metals which isrelatively refractory and resistant to abrasion at high temperatures.

It is a particular object of the invention to produce an inter-metalliccompound of silicon and molybdenum in which these components arecombined in the stoichiometric proportions of molybdenum di-silicide(Mosi It is an additional object of the invention to produce adi-silicide of molybdenum which by methods of powder metallurgy may bemolded and shaped into products that are resistant to oxidation, are ofaccurate dimensions and relatively high mechanical strength.

An object also is to provide a composition formed by a mixture of adi-silicide of a metal selected from the group consisting of uranium,molybdenum, chromium, tungsten, zirconium, and titanium, with othermetals, semi-metals, oxides, carbides, borides or other silicides.

An additional object of the invention is to produce a compound ofsilicon having high corrosion and wearresistant properties.

Prior scientific and patent literature contains various suggestions forthe production of molybdenum disilicide. However as far as the inventoris aware, there was not available up to the present time a simpleprocess for producing molybdenum disilicide of relatively high purity ina form in which it could be readily comminuted into fine particles foruse in producing by powder-metallurgy technique shaped cemented bodiesof great hot strength and corrosion resistance.

The present invention is based on the discovery that, when astoichiometrically proportioned intimate mixture of fine particles ofmolybdenum and silicon, corresponding to the formula Mdsi is heated toan elevated temperature of about 2000 R, which is well below the meltingpoint of these components, a reaction takes place between them whichresults in the production of relatively pure molybdenum disilicide in afriable form which may be readily comminuted into fine powder particlessuitable for powder metallurgy processing. The reaction of the siliconwith the molybdenum is exothermic and the .temperaturerises to about3000 F. Thesilicon reacts with the molybdenum throughout the mass and Inparticu-- forms a new lattice structure. This isshown by X-raydifiraction tests which show the disilicide pattern present, and silica..When the reaction is run in a vacuum or a reducing or inert atmosphere,the excess silicon appears as silicon and not as silica. I

This inventor has produced the molybdenum disilicide in powdered formfor use in molding various articles by the difierent methods of powdermetallurgy. He obtained the disilicide in powdered form by mixing oneequivalent of powdered molybdenum with two mols;

. equivalents of powdered silicon (325 mesh size), thoroughly mixingthis mixture as in a ball mill, removing the mixture from the ball milland heating the stoichiomet; rically proportioned fine mixture in air,vacuum or inert gas atmosphere until an exothermic reaction occurred Asuitable v'esselof refractory material, such as a crucible or boat ofalundum, beryllia, etc., may be used for holding the powder mixturewhich is produced in the 'furnac'eQ This reaction took place at aboutl900 F.:L100 F. with a subsequent temperature rise to about. 3000 F. Thepowder was then crushed, ball-milled and leached with concentratednitric acid to remove any unreacted molybdenum metal and with hothydrochloric acid to remove any molybdenum oxide. Leaching is notnecessary when reacting in a vacuum or gas atmosphere. It was found thatthe silicon volatilized at the reaction tem perature under a vacuum;that it was necessary to carry the reaction to completion in a partialpressure atmos-- phere of argon or helium when such gas was introducedinto the vacuum to furnish up to one half to three quarters atmosphericpressure.

' techniques yield a cemented body of substantially pure molybdenumdisilicide (Mosi exhibiting extremely desirable hot, physical andmechanical properties, which combined with its superior corrosionresistance makes it ideal for applications such as gas-turbine buckets,flame holders and the like. V

This inventor produced the disilicides of metals otherthan molybdenum bythis direct reaction method. In particular he produced the disilicidesof uranium, chromium, tungsten, zirconium, and titanium. These silicidesvary from one to the other in their physical properties andconstruction. They vary in refractoriness and in resistance to oxidationat high temperature. But all are useful in certain applications.

A second method of powdered metal preparation in which powderedmolybdenum disilicide, prepared as i above described, is impregnatedwith other metals such as copper, nickel, cobalt, etc. or other alloys,such as Colomonoy No. 6, Phosphor bronze, etc. In. this method ofpreparation these additive metals and alloys are drawn into the'skeletonof the molybdenum disilicide to form an intimate material. These alloysare not as refractory as the molybdenum disilicide alone, but they areuseful for the reason that they can be readily worked by the process ofhot forming i.e. hot coining. Y

5 mogeneity and simple stoichiometricproportions with aesae 1e atoms ofidentical kinds occupying identical points on the Titanium 46.05 7Silicon 53.95

the analyses of powdered silicides, prepared as above described gave thefollowing:

In neither case are the titanium and silicon present in the theoreticalproportions. Thesecompounds, however, showed good results at elevatedtemperatures and must be considered only as intermediate solidsolutions.

Tungsten disilicide, as produced by the method of this inventor is atrue intermetallic compound, checking very close to stoichiometricproportions. For some reason, not at present known, this compoundalthough highly refractory, is not as resistant tooxidation as the otherabove listed disilicides. Its use is therefore limited to hightemperature operations where oxidizing conditions are not too severe.

The use of these powdered disilicides is extensive. They may be used asa protective coating on other metal bases.

alloyed with other metals or semi-metals to form articles of simple orrelatively complicated shape by the methods of powder metallurgy.

As a protective coating on other metallic bases, molybdenum disilicidemay preferably be applied in one of three ways:

(1) As a coating on molybdenum, silicon is applied as a coating on apiece of molybdenum, the coated piece is then heated to a temperature atwhich diffusion occurs, and the silicon diffuses into the molybdenumthereby forming a strong bond for the coatingto the base metal.

(2) The application of a disilicide of one of the metals of the abovedefined group, for instance, molybdenum disilicide as a protectivecoating on the surface of a base material. The coating is applied byspraying the powdered silicide by means of a powdered metal spray gun inan atmosphere of helium, argon, nitrogen, or hydrogen under a pressureof from five to eight atmospheres and subsequently difiusing thedisilicide into the base material in an inert gas atmosphere or vacuum.

(3) The disilicide is worked up in a carrier medium and applied as abrush coat on the surface of the base metal. The coated metal is thenbaked at a high temperature, in an inert atmosphere or vacuum to diffusethe disilicide into the surface of the base metal thereby forming astrong bond for. the disilicide coating.

The fabrication of the powdered disilicides of the group ofmetals abovedefined, and of molybdenum in particular, can be accomplished by anumber of methods for example as follows:

(l). Cold. pressing and sintering.

.(2) Harnessin (3) Vacuum casting.

(4) Hot coining.

(5) Swaging and rolling.

The formed material canbe machined and brazed to the final requiredforms by methods such as:

(1) Grinding, diamond or gravity fed silicon carbide wheel. V

(2) Machining, using carbide tools (only when in a partially sinteredcondition).

( 3) Brazing, using silver, copper or colomonoy alloys.

PRODUCTION OF ARTICLES BY THE METHODS OF POWDER METALLURGY As statedabove, the production of articles by the methods of powder metallurgycan be accomplished by fine basic methods. The first of these, coldpress and sinter, because of its extensive use industrially will bediscussed first.

The cold press and sinter method This method is now used commercially inthe fabrication of cemented carbides. This method, with somemodification, can be used for the making of articles from the powdereddisilicides of this invention and particularly for the molding ofpowdered molybdenum disilicide.

In this process cold pressing is accomplished by the use of properlyshaped permanent dies and applied pressure. The dies are oversized toallow for shrinkage during sintering. The pressure used varies with theshape of the work, the organic binder used, and the compacting necessaryfor good, green, mechanical strength. The pressure must be uniformlyapplied over thcentire die in order to increase the resistance topossible later thermal shock. The pressures used vary between about tenand thirty tons per square inch. After the compacted piece is removedfrom the press it is sintered at a relatively high temperature about2700 F.-3l00 F. either in a vacuum or an inert atmosphere'such as argonor helium. This inventor found that hydrogen, although widely used incommercial processes of sintering cemented carbides, cannot generally beused without some difficulties with pure molybdenum disilicide bodies;but that hydrogen could be used as a reducing atmosphere in thesintering step if small additions of binder metals, such as nickel andcobalt, were made to the powdered disilicide. The use of a hydrogenatmosphere is very desirable because of the relatively low cost and itscommercial use.

The use of binder metals such as nickel and cobalt permits hydrogensintering atmospheres and sintering temperatures up to about 2600 F.Above this temperature cracking occurs. The addition of iron or chromiumas a binder metal lowers the sintering temperature to about 2430 F.,above which temperature cracking occurs.

Particle size of the disilicide powder is important in the cold pressand sinter method for. the effect it has on the density and mechanicalstrength of the sintered body. While not, as yet, completely determined,test data indicate that a particle size of from one to about six micronsis desirable.

The cold press and sinter method includes the conventional processes ofextrusion and slip-casting. In the extrusion process a powder extrusiongun is used. The powder (the disilicide), after being mixed with organicbinders, such as starch, glycerine, waxes, etc. is extruded throughspecific dies. The extruded parts are then slowly heated from lowtemperatures to maximum sintering temperatures. This process isparticularly applicable in the fabrication of tubes. The slip-castingprocess may be used for making odd and complicated shapes and forms ofthese disilicides. A slurry is made with organic binders and cast intomold, after drying the shape is sintered slowly as in the extrusionprocess.

The hot press method Th dis l de t h me ls bc e defin d may s be moldedand shaped inipowdered form by the hot press method. In particularmolybdenum disilicide, *which.

may be prepared with a purity of about 99.8%, may be molded by thismethod. For successful use in this method of pressing, the powder mustbe ground to a TABLE I 4 V V Percent of Particle Size Total 0-6 microns.90 400 6-26 microns- 0-10 Test data indicates that as regards tostrength at least 90 percent of the particles must be less than 6microns 7 in diameter.

The powder upon removal from the ball mill must be completely dried andwhen necessary leached with dilute hydrochloric acid to remove metalliciron which may have been picked up during ball milling.

The powder is then pressed to the shape desired by the use of graphiteform molds. The temperature used for hot pressing may vary between 2600F. and 3100" F. Because of commercial limitations it is more practicableto use temperatures within the range of 2700" F. to3000F.

The pressure used for hot pressing may be varied generally from 500 to7000 pounds per square inch depending upon the strength of the graphitedies and the temperature used for pressing.v The relative brittleness ofthe disilicide, however, increases with increase in the applied pressureto the maximum allowable with the graphite dies. It is therefore moredesirable to use pressures near the mean of the pressure limits forreasons of costas well as less brittleness. The density of thedisilicide also generally increases with the pressure and a pressure offrom 1000 to 2000 pounds per square inch is required to obtain a densityof over 5.0 grams per cubic centimeter when using fine powder (90% lessthan 6 microns).

Prolonged soaking at the temperature of hot pressing 7 increasesslightly the shock resistance or toughness of the disilicide at roomtemperature. Pressing and soaking at temperatures'of 2900-3200 F. have agreater elfect on shock resistance or toughness of pieces than onsamples pressed and soaked at lower pressing temperatures. Ap-

parently the pressing temperature is the effective variable in thecontrol of this physical characteristic. 7

The fractured disilicide, when hot pressed under th optimum conditionsof temperature, pressure, particle size and particle size distribution,has a fine grained; silky, satiny luster similar to that obtained whenhot-pressed cemented tungsten carbide is fractured. I Q V The density ofthe hot pressed molybdenum disilicide may be varied over the range offrom 5.00 to about 6.15

grams per cubic centimeter by 'variation in the follow ing physicalcharacteristics of the components and factors in the method of pressing:

a. Particle size.

b. Particle size distribution.

.c. Pressure. I

d. Temperature of hot pressing.

The density for maximum strength properties varied between 5.80 and 6.15grams per cubic centimeter with 5.80 to 5.95 being the more desirabledensity figure. The I high density limit may be attained by:

a. A fine particle size' with non-uniform particle size t distribution.vj

microns) b. A lower hot press pressure and a lower hot press temperatureor 10 a c. A combination of both. Reference to Table 2 shows that thedensity of the 'molybdenum disilcide can be varied by merely varying theparticle size and the particle size distribution and that 'with adecrease in densityfldueto. an increase in ,fineness of particle sizeand a more uniform particle size distribution there is a drop inftheful'tim'ate breaking strength at the same temperature.

The above described hot-press'procedures'have' been used for makingvarious fabricated parts, such as flameholder plates, turbine blades'andbars.

Vacuum casting It has not been possible to produce porosity-free bars ofmolybdenum disilicide by this method. Experimental tests, however,indicate that this disilicide can be cast in a positive pressureatmosphere of an inert gas, i.e. argon or helium.

It was found that zircon crucibles could be used satisfactorily for themelting and that in connection with porosity developed in bars cast invacuo this leads to gas entrapment in the body of the casting; that hotpress slugs also contain a considerable quantity of entrapped gas andthat in powdered cold-press and vacuum sintered slugs the largest partof entrapped gas is eliminated.

In its present state of development the vacuum casting process isbelieved to be too costly for extensive use.

Hot coining This method of fabrication is a finishing process which froman economical standpoint is highly advantageous. It is similar to hotpressingan already particularly sintered part. A part could therefore becold-pressed and partly sintered to shape and then hot forged or hotcoined to the final exact shape. This operation accomplishesdensification, dimensional stability and eliminates or minimizes finishmachining operations.

Swaging and rolling The following requirements. for effective swagingand rolling have been experimentally determined:

ayHigh purity of material is required, otherwise, the material is hotshort and cracking occurs.

b. Fine uniform particle size is required percent less than 3 microns.in diameter).

0. Swaging temperature preferably should be in excess of 2800 F., butnot greater than 3100 F. d. Percent reduction should be at a slow rateinitially.

MECHANICAL PROPERTIES AT ROOM AND ELE- VATED TEMPERATURES OFHOT-PRESSED.

MOLYBDENUM DISILICIDE I In the followingtable are given test data on thechange in ultimate breaking strength from that at room temperature tothat at 1800, 2000, 2200", and 2400 vF. on rods of molybdenum disilicidewhich were formed by the hot-press method and which varied in particlesize and particle size distribution as indicated.

TABLE 2 22 I or must be noted, however, that increase in ductility isaccompanied by a decrease in high temperature strength,

Purity,

Particle Size (Microscopic Count).

. Percent Density, g./cc.

Test Temperature, cl

Total elongation Percent in 3" 100% 15 microns, 5c% 5 microns Room Temp"Not Detectable. Do.

Do: 0.1 percent. 0.5 percent.

1 Broke in grip collet. 9 Pulled through the high temperature grips.

No'rn.-The increase in elevated temperature tensile strength from thestrength at room temperature is due to better alignment and fit of allgrip material and specimen at the elevated temperatures.

It could also be due to an increase in the disiliclde ductility as thetemperature increased (this ductility could be vcr% little and notdetectable by ordinary measuring methods).

It is also possible that this increase is due to a di usion process inthe disilicide at elevated temperatures. Tests are ncw ln progress toascertain whether or not this is true.

The decrease in density with increase of uniformly distributed anddecreased range in particle size is noted. The increase in ultimatebreaking strength from that at room temperature to that at elevatedtemperatures is relatively great. This may be due to several causes ofnone of which is the inventor certain. This increase may be due to:

a. Better alignment and fit thespecimen.

b. An increase in ductility of the disilicide.

In other words this table shows generally that:

As the particle size decreases,

a. The elevated temperature breaking strength increases.

b. The ductility increases.

0. The density decreases slightly.

As the particle size distribution becomes more uniform,

a. The elevated temperature breaking strength decreases attcmperatnresat and above 2200 F.

b. The ductility at elevated temperatures increases.

c. The density tends to decrease slightly for similar pressingconditions. 7 v

In general it may be concluded from the data in Table 2 that:

a. The ultimate breaking strength of the material remains approximatelyconstant from room temperature to 2400 F. provided that the particlesize and particle size distribution are as that shown in Table 1.

b. The ductility of the material increases at elevated temperaturesprovided that particle size and particle size distribution are as shownin line 1, Table 1.

c. The ultimate breaking strength of they material decreases above 2200F. and the ductility increases provided the particle size is 100 percentless than 6 microns and uniform in distribution (90 percent to 95 percenless than 3 microns in diameter).

,.Ductility is an importantcharacteristicinmany applications and uses ofthis material. This isthe property which decreases the notc sensitivity,relieves initial thermal stresses, and facilitates commercial handling.

of all grip material and and that ductility at room temperature cannotbe detected. THERMAL EXPANSION Determination of the cumulative thermalexpansion of triangular prisms of molybdenum disilicide was made throughthe temperature range of room temperature to 1500 C. followed by areverse determination of from 1500 C. to room temperature. Theparticlesize of the sample is as shown in Table 1. The density of the sample was5.93 to 5.94 grams per cubic centimeter. The test results are given inTable 3.

TABLE 3.LINEAR THERMAL EXPANSION- CUMULATIVE PERCENT It is noted thatthe material had a linear shrinkage of .08 percent upon cooling to roomtemperature. This is due to an additional sintering action occasioned bythe heating to 1500 C.

AIR CORROSION PROPERTIES This inventor has found that molybdenumdisilicide is very resistant to corrosion, i.e. oxidation in air atelcvated temperatures. Pieces of this disilicide ofknown area were heldin a furnace, in an atmosphere of air,,

at temperatures of 2200, F., 2450 F., and 2850" F., for hour, 200 hour,and 300 hour periods. of time.

' cemented carbides.

9 I The pieces were then cooled weight was determined. The results aregiven inrthe following table:

Examination of this table indicates that there is very little effect ofair corrosion on the molybdenum disilicide: at elevated temperatures.temperatures (below 2500 F.) there is a weight gain, while after heatingat the higher temperature there is a Weight loss; This is due to themovement of a sec-. ondary impurity phase to the surface and the burningor volatilizing away of portions of this phase as it reaches thesurface.

- Electron diffraction photographs of the surface before. andafterheating has shown the presence of an amorphous phase on the surfaceafter heating at 2850 F. This can be removed by slight polishing and thecrystalline pattern of molybdenum disilicide surface returns.Metallographic analysis shows the loss of the secondary phase to thesurface from the interior, which substantiates the electron difiractionand corrosion results.

The minute secondary phase thus accounts for the change in weight uponheating in the tests conducted. It is believed that by theelimination ofthis phase, the

and the gain or loss in is one of the most important problems relatingto molybdenum disilicide],

. .The basic reason for these metallic additions is to in crease thetoughness or decrease the inherent brittleness of the intermetalliccompound. Preliminary tests showed that iron, nickel, cobalt, chro-'ninrn, and platinum wetted the molybdenum disilicide, therebyindicatingdefinite possibilitieslfo'r good alloying "toughening characteristics.

It is noted that at the lower air corrosion resistance properties willbe, much better than that shown and that the physical properties willalso be improved.

I CHEMICAL CORRODIBILlTY At normal temperatures molybdenum disilicide isrelatively inert or non-reactive to acid or basic re-agents. Table 5shows the percentage loss in weight per hour of thisdisilicide inreaction at 70 F. with two concentrations of nitric acid, hydrofluoricacid, sulphuric acid, hydrochloric acid and sodium. hydroxide.

' .IABLE 5.CHEMICAL CORRODIBILITY 0F MOLYBDENUM DISILIOIDE AT 70 F.

7 [Percent change in weight per hour] ema a i n HNO; HF ms o. H01 NsOH10%--. O. 0034 0. 0019 0. 0005 00l-2 Concentrated 0. 010 0. (1012 0.0005 0. 0001 resistance to abrasion'ofthis'material with its excellentphysical strength and'resistance to corrosion, all at elevatdtemperatures, opens up a rather extensive field of application in itsuse. r

ME A L 'ADD I The use of other metals. to form homogeneous alloys or toform a fcementing phase heterogeneous material Oxidation tests indicatedthat for temperatures up to' :2600" F. an alloying content up to 20percent of cobalt .....was possible without too great a deterioration.The rela- ,tive toughness comparison of 5, 10, and 20 percent additionsof cobalt indicated that the 5 or. '10-.percent addition was better thanthat of the 20 percent. Also short time oxidation tests at 2800" F.showed that the addition. of 5 to 10 percent of cobalt did not affectthe resistance to oxidation properties appreciably.

Investigations were therefore conductedon the basis of using from 7 to 8percent metallic additions of co-" balt, nickel and platinum. The finemolybednum disilicide powder was ball-milled in benzeneand/ or alcoholor acetone with these metallic additions for seventy two hours anddried. Bars of the material were hot pressed at temperatures above themelting points of the alloying metals. Dlfiiculty was encountered withthe cobalt addition and many of the bars containing this additivewerecracked after the graphite die had cooled. The nickel and platinum barsdid not crack and manufacturing con- ,ditions indicated that the nickeladdition was best 'for' handling. The 7.5 percent nickel bars weremachined into tensile strength specimens and weretested at 2000" F. Theresults showed an ultimate strength of only 4,000 pounds per squareinch, as compared to 40,000-

should be reduced to the range of from l'to 4 percent for maximumtensile strength. Thus in Table 6 is shown the variation in ultimatetensile breaking strength of molybdenum disilicide specimens each onecontaining additions of 3.3 percent by Weight of iron, cobalt, nickel,

and chromium, respectively. These specimens were cold.

pressed and sintered at the temperatures indicated, viz. 1250 C., 1300C., 1350 C., 1400 C., and 1450 C.

in an atmosphere of hydrogen and also at 1450. C. in

vacuo.

It should be noted that, in general, the nickel addi-" tion gave thehigher modulus of rupture values partic-" ularly for the specimenssintered at 1300 C. and 1350 C. Also it should be noted that with arelatively small" addition of these alloying metals these results wereobtained on specimens which had been sintered in an atmosphere ofhydrogen. This makes commercially available various shapes and forms nototherwise available at reasonable cost.

Other elements Wereadded for the express purpose of cleansing thedisilicide particles. of oxygen or other gases.

These additions amounted to from 0.1 percent-2.0 percent and consistedgenerally of getter elements. Ex.

titanium, zirconium, carbon, etc. These additions would tend .toincrease inter-particle cohesiveness, and thus an increase in thestrength of the bodies was noted.

NON-METALLIC ADDITIONS (l) borides and other silicides on the order offrom 0.1 per cent to 35 percent additions to the disilicide bodies isThese additions are made .to incr'ease the elevated temperatureproperties of the disilicide bodies for specialized purposes.

practical.

As a result of, the above tests it was decided that the alloy addition'The addition of small amounts of oxides, carbides,

anaemic TABLE 6.MEIALLIO ADDITIONS-SINTERING EFFECT 1,450 O. (Vac) Iron:

Trans. Strength (p.s.l.) Cracked Hardness (Rx) 48. 400 Broke. 16

Shrinkage Density NON-METALLIC ADDITIONS (2) The use of molybdenumdisilicide as a binder metal for very hightemperature applications (3000F. to 5000" F.) with such compounds as beryllia, alumina, and the metalcarbides is practical.

Tests were run using BeO (beryilia) and A 6 (alumina). Samplescontaining up to percent of molybdenum disilicide were hot pressed at atemperature above that of the disilicide. The compacts were then heatedin air in an induction furnace to temperatures in excess of 3800" F.Little effect was noted on the samples and the use of this type ofceramal for very high temperature use looks promising.

Disclosure has been made of a preferred method of compounding thedisilicides of certain metals of the fourth and sixth groups of theperiodic table. The method disclosed does not involve the completefusion of the base metal and the silicon as is done in the prior art. Inthis mventors method the silicon upon reaction with the base metalenters the lattice structure thereof forming either a definite compound,an intermetallic compound or an intermediate solid solution therewith.Inasmuch as it is sometimes desirable to have a small excess of siliconpresent and at other times a small excess of the group element present,variations from the particular proper tions given supra can be madewithout departing from the spirit or scope of the invention beyond thatas defined by the herewith appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor. This is acontinuation of application Serial No. 177,548, filed August 3, 1950,now abandoned.

What is claimed is:

1. An article of manufacture comprising a sintered powder metallurgyproduct consisting essentially of sintered powder particles selectedfrom the group consisting of the disilicides of uranium, molybdenum,chromium, tungsten, zirconium and titanium powdered substantially 100%to particle sizes substantially less than 25 microns.

2. An article of manufacture comprising a sintered powder metallurgyproduct consisting essentially of sintered powder particles selectedfrom the group consisting of the disilicides of uranium, molybdenum,chromium, tungsten, zirconium and titanium powdered substantially 100%to particle sizes substantially less than 25 microns; at least 90% ofsaid particles having a particle size less than 6-microns;

[3. An article of manufacture comprising a sintered powder metallurgyproduct consisting essentially of sintercd molybdenum disilicide powderparticles powdered substantially 100% to a particle size less than 25microns, said product having a density ranging from 5.00 to about 6.15grams per cubic centimeter.

4. A process for forming a sintered powder metallurgy product consistingessentially of sintered powder particles selected from the groupconsisting of powder particles of the disilicides of uranium,molybdenum, chromium, tungsten, zirconium and titanium, said processcomprising forming said disilicides in each instance by heating anintimate mixture of the elements thereof in powder form to a temperatureinitially less than the meltingtemperature of said elements and highenough to initiate reaction between said elements and allowing saidreaction to proceed tosubstantial completion and produce a disilicide ina friable form and thereafter milling said friable disilicides to saidpowder particles to a degree reducing them to a particle sizesubstantially less than 25 microns; and forming said disilicide powderparticles to the desired shape of said product and heating the resultingshape to sinter said disilicide powder particles.

5. A process for forming a sintered powder metallurgy product consistingessentially of sintered powder particles selected from the groupconsisting of powder particles of the disilicides of uranium,molybdenum, chromium, tungsten, zirconium and titanium, said processcomprising forming said disilicides in each instance by heating anintimate mixture of the elements thereof in powder form to a temperatureinitially less than the melting temperature of said elements and highenough to initiate reaction between said elements and allowing saidreaction to proceed to substantial completion and produce a disilicide.in a friable form and thereafter milling said friable disilicides tosaid powder particles to a degree reducing them to a particle sizesubstantially 100% less than 25 microns and at least.90% to a maximumparticle size of 6 microns; and forming said disilicide powder particlesto the desired shape of said product and heating the resulting shape tosinter said disilicide powder particles.

6; A process for forming an article of manufacture comprising a sinteredpowder metallurgy product consisting essentially of sintered powderparticles selected from the group consisting of powder particles of thedisilicides of uranium, molybdenum, chromium, tungsten, zirconium andtitanium, said process comprisingforming said disilicides in eachinstance by heating an intimate mixture of the elements thereof inpowder form to a temperature initially less than the melting temperatureof said elements and high enough to initiate reaction between saidelements and allowing said reaction to proceed to substantial completionand produce a disilicide in a friable form and thereafter milling saidfriable disilicides to said powder particles to a degree reducing themto a particle'size substantially 100% less than 25 microns; coldpressing said disilicide powder particles to form an unsintered piecehaving the desired shape of saidprodnct, and sintering said piece toform said product.

7. A process for forming an article of manufacture 13 comprising asintered powder metallurgy product consisting essentially of sinteredpowder particles selected from the group consisting of powder particlesof the disilicides of uranium, molybdenum, chromium, tungsten, zirconiumand titanium, said process comprising forming said disilicide in eachinstance by heating an intimate mixture of the elements thereof inpowder form to a temperature initially less than the melting temperatureof said elements and high enough to initiate reaction between saidelements and allowing said reaction to proceed to substantial completionand produce a disilicide in a friable form and thereafter milling saidfriable disilicides to said powder particles to a degree reducing themto a particle size substantially 100% less than 25 microns; placing saiddisilicide powder particles in a mold and applying high pressure andheat to said particles in said mold so as to hot press and sinter saidparticles in said mold to form said product to the shape of said mold.

8. A process for forming a sintered powder metallurgy product consistingessentially of sintered powder particles of molybdenum disilicide, saidprocess comprising forming said disilicide by heating an intimatemixture of the elements thereof in powder form to a temperatureinitially less than the melting temperature of said eleabove the brittletemperature range of said sintered diments and high enough to initiatereaction between said 2 elements and allowing said reaction to proceedto subsilicide shape, and while said shape is thus heated hot Workingsaid shape to the ifinal desired shape of said product.

References Cited in the file of this patent UNITED STATES PATENTS1,560,885 Walter NOV. 10, 1925 2,089,030 Kratky Aug. 3, 1937 2,116,400Marth May 3, 1938 2,193,413 Wright Mar. 12, 1940 2,665,474 Beirdler Jan.12, 1954 2,779,580 Steinitz Ian. 29, 1957 2,921,861 Wehrmann et al Jan.19, 1960 FOREIGN PATENTS 435,754 Great Britain Sept. 23, 1935

1. AN ARTICLE OF MANUFACTURE COMPRISING A SINTERED POWDER METALLURGYPRODUCT CONSISTING ESSENTIALLY OF SINTERED POWDER PARTICLES SELECTEDFROM THE GROUP CONSISTING OF THE DISILICIDES OF URANIUM, MOLYBDENUM,CHROMIUM, TUNGSTEN, ZIRCONIUM AND TITANIUM POWDERED SUBSTANTIALLY 100%TO PARTICLE SIZES SUBSTANTIALLY LESS THAN 25 MICRONS.